1. Field of the Invention
The present invention relates to a 1/2 wavelength side coupling filter and, more specifically, to a 1/2 wavelength side coupling filter employed in, for example, a low noise converter for receiving satellite broadcasting.
2. Description of the Prior Art
FIGS. 1 to 3 are patterns of microstrip lines in conventional 1/2 wavelength side coupling filters.
First, referring to FIGS. 1 to 3, description will be given of a conventional 1/2 wavelength side coupling filter. In FIG. 1, a plurality of resonance lines 4 are arranged on a printed board 20 in parallel to each other in the horizontal direction in a staggered manner. An input coupling line 3 is arranged adjacent to the resonance line 4 on one end. A signal input end 1 is formed extending from the input end 5 of the input coupling line 3, and signals are inputted to the signal input end 1. The end portion 6 of the input coupling line 3 is formed such that it is aligned with an intermediate position of the resonance line 4. Only the signal components in a prescribed band out of the signals inputted to the input end 1 are outputted from an output end 2 of the resonance line 4 of the last stage.
The length from the input end 1 to the output end 2 of the 1/2 wavelength side coupling filter structured as described above should be longer than a prescribed length. However, if other parts and the like are arranged in the x direction limiting the space, the arrangement of the pattern shown in FIG. 1 cannot be employed.
In the 1/2 wavelength side coupling filter shown in FIG. 2, the input coupling line 3 and a plurality of zonal resonance lines are arranged in the vertical direction, with the input end of the input coupling line 3 bent by 90.degree. in the horizontal direction, and the output end 2 of the resonance line 4 in the last stage bent by 90.degree. in the horizontal direction. The 1/2 wavelength side coupling filter of this pattern arrangement is advantageous when there is a limit in the x direction but not in the y direction in arranging the pattern on the board 20. However, if other parts are arranged in the y direction, it is disadvantageous if the space is taken into consideration.
Since the limit of space makes it difficult to arrange the 1/2 wavelength side coupling filters shown in FIGS. 1 and 2, a pattern arrangement such as shown in FIG. 3 can be resorted to. In the example shown in FIG. 3, the input coupling line 3 and a plurality of resonance lines 4 are arranged with inclination, with the input end 1 and the output end 2 bent so as to be oriented in the horizontal direction. The 1/2 wavelength side coupling filter having such pattern arrangement is more available than the examples shown in FIGS. 1 and 2, even if the space is limited both in the x and y directions. However, the filte has a disadvantage such as follows. The 1/2 wavelength side coupling filter shown in FIG. 3 has its input coupling line 3 and the resonance lines 4 formed by etching. In order to make an original drawing for fabricting films for etching, the angle factors in the x and y directions are required, the check for each of the coordinates becomes complicated, and the check of modification of the dimension becomes difficult.